Heating process



Dec- 7, 1943 H. F. HowARD Erm. -2,336,177

-HEATING PROCESS Filed July 11, 1941 2 Sheets-Sheet l De@ 7, 1943. H. F. HOWARD ETAL 2,335,177

HEATING PROCES S Patented Dec. 7, 1943 HEATING PROCESS Harold F. Howard and William Richards, Flint,

Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Y v Application July 11, 1941, Serial No. 401,888

1 Claims.

The "present invention relates to the method of manufacture of valves and the like consisting of heating one end of a rod to forging heat and then forging the end into the shape of the head of the valve. y In order to confine the heating 5 to one portion of the rod, avoid the formation of scale, and secure other .advantages later dis, cussed, heating is done by means @thigh frequency electricity. The present invention has to do with improvements in the method of heating disclosed in our copending application filed October 7, 1938,-now U. S. Patent 2,275,763 granted March l0, 1042.

In early work with this method use was made of rotary generators producing comparatively W frequency current, i. e., on the order of three kilocycles and it was found that small, restricted. portions of the rods could not be heated to forging temperature in the desired short period of time. Nor were satisfactory results obtained by employing substantially higher frequencies, e. g., on the order of five kilocycles.

Experimentation with higher frequencies soon revealed that even doubling or trebling the frequency failed to give the rapid ferrous-stock heatingfdesired because of the fact that when a temperature inthe neighborhood of 1200 F. was

` dno further heating took place for the 1200 F. is in lthe neighborohood of point for the steel employed, that is, caltemperature above which the magy A y eability is very small. Because of the abrup ling olf of magnetic permeability it appearedfthatjthe frequencies required to heat the metal arboveits Curie point would be so high as to befir'npracticable to attain because of thefcost andiinelciency of the electrical equipment "e'mpioyerl:y l `-Aft`er much research and experiment, applicantsfdiscovered that rods of 1%, alloy steel such a'sf'is employed for internal combustion engine valves might be terminally or otherwise restrictively locally Iheated to forging temperature (2000 F.) in 7.5 seconds by subjecting the rod Aportion to be forged to the magnetic field induced in an air-core winding energized by an undamped current of ultra-high frequency, i. e., above the 10,000 cycle-per-second limit conceded by'authorltles to be the practical upper limit for rotary alternators of the Alexanderson and'Goldschmidt types employed for heating on a production scale. As fully brought out in our co-` pending application, now Patent No. 2,275,763, the time-'available for heating such rod stock must be"`prac tically momentary to preclude the 55 during forging are realized. In accordance with this invention, only that portion of the rod which is to be forged is heated to a degree of plasticity such that warpage or other deformation may occur. Still further, since with such instantaneous heating'material conduction of heat throughout the valve 4blank is precluded prior to forging,

the operator is able manually to transfer the blank from furnace to the forging press and thence to the bin or conveyor by bare hand without suffering the slightest burn or discomfort.

In applying their discovery to the heating of alloy steel rod stock for fabricating valves and the like, applicants found that undamped currents having a frequency of from 125,000 vto 140,000 cycles per second effected uniform through heating of alloy-steel rod stock having a diameter of of an inch in a matter of seconds,` a forging temperature of 2000 F. being realized in appro imately 7 to 8 seconds of time. For a disclosurel ja lpreferred embodiment of their invention,"reference is made toA themaccon panying drawings, wherein: y K

Figure 1 illustrates diagrammatically the electrical equipment employed. Figure 2 is a' longitudinal sectio-n through the heating coil assembly.

Figure 3 is a fragmentary view taken on line v3--3 of Figure 2.

Figure 4 is Va fragmentary view taken on line 4--4 of Figure 2.

In the case of the Valve rod heating operation referred to, a suitable source of electrical energy such as a 3 phase, 4800 volt, 60 cycle power line is indicated in Figure 1 as supplying energy to a, step-up transformer preferably having a 1:3 ratio of transformation supplying a suitable rectier, preferably of the type employing two element tubes, which in turn supplies rectified current at approximately 8500 volts to a. suitable vacuum tube oscillator unit as indicated. A separate 220 volt, 3 phase, 60 cycle supply is used for the tube laments and for auxiliary apparatus such as the pump supplying cooling Water to the oscillator and coils H through a suitable high frequency transformer T, the secondary of which supplies current preferably through a coaxial cable indicated at C to a plurality of heating coils H arranged in series. The coaxial cable consists of coaxial tubular conductors separated by ceramic insulators in accordance with conventional construction. Suitable controls are provided for the rectifier and oscillator and the usual switches, relays and timers, fuses, circuit-breakers and the like may be employed as desired. Watercooling is provided as usual for the oscillator and coils H.

Provision may be made for adjustment of the oscillator circuit to produce the frequency desired. The oscillator and the oscillator output circuit must be very carefully shielded to prevent interference with radio receiving and broadcasting for the oscillator itself constitutes a powerful radio sending station, lacking only a suitable antenna and modulation to render it usable i water may 'be circulated through them through input connection I8 and output'connection `20 .from a suitable pump, not shown.' Coils H are surrounded by jackets 22 of insulating material and are lined withvsleeves 24 likewise of insulat- -ing material, the coils and linings being mounted on insulating supports 25 and p0sitioned vat the opposite ends by insulating bushings 26. From the latter tubular insulators 28 extend to the outside of the box to permit ready insertion to the parts to be heated.. Suitable meansv may be provided to limit the extent of inward movement of the valve rod stock into the heating coils.l We

havevk indicated diagrammatically a-support 30 f carrying supporting pins 32. It is t0 be understood that the parts last described, together with4 the insulating sleeves, liners and supports arel constructed of material'having not only good Y electrical insulating properties but also high re-V sistance to heat. For this purpose we may employ insulating material made of various refractory oxides or mixtures of oxides.

In heating the rod it is but necessary to insert it in one of the coils H, as indicated at R in Figure I2, and in seven oreight seconds withfapparatus of .the capacity next specified the rod end will be heated to the desired forging temperature. It will be noted that the work circuitis illus;

trated as atuned circuit, condenser I0 being of sufficient capacity to eect tuning when a valve` rod is being heated in each ofthe coils H. When there are no valve rods in the coils the circuit is completelyl detuned so that very little current ilows in the load circuit and the energy consumed in the heating'equipment is likewise `verysmall.l

In heating diameter valve rod stock to approximately 2000 F. in approximately eight seconds, it has been founda desirable to use frequencies of from v125,000 to 140,000 cycles, preferably the latter. A power input of approximately 125` kv.a. is required. Therheatingcoil current is preferably on the order of 20. amperesl It -will bel understood that the figur i.

sttute but one specific example ofthe application of our invention.

In general, ultra-high frequency current may be employed according to our invention for the heating of any and all metals to forging or welding temperatures or, if desired, by use of higher frequencies toaccomplish melting. The method is just as applicable to non-ferrous or non-magnetic materials'fas it is to ferro-magnetic materials for the major portion of the heating is accomplished by resistance to the iiow of eddy currents ratherthan by hysteresis effect.

This method of heating possesses many advantages:

The cost per heating unit actually used in v heating thel stock is -relatively low. This is because the equipment does not consume any substantial amount of energy except when the metal is being heated in the coil and, since the equipment contains no moving parts, the maintenance cost is negligible as compared with the maintenance cost of furnaces, resistance Welders or otherl conventional forms of heating apparatus. It has previously been pointed out that the process gives an improved product free from scale and thereby lengthens die life. No complicated temperature controlling apparatus is required as it is but necessary to properly adjust the gener.- ating unit to give the ldesired heat output in the time cycle required. vBecauseof these and other advantages it is expected that a multitude of uses of lultra-high frequency heating will develop in manufacture.,

We. claim: y A 10-second forging method for solid ferrous rods such as internal combustion engine valve blanks of diameter which are subject to diedestructive rapid scale formation at forging temperatures of 2000 F., comprising: placing the portion ofthe solid ferrous rod whichis to be forged inside an air-core winding having magnetic field definition closely corresponding to the `rod portion to be`forged, energizing said winding from a source of undamped oscillating current having a frequency on the orderof 125,000

cycles per second and a value of approximately 100 kv.a. perounce of said rod portion to be forged, maintaining said rod portion within the field produced by said thus-energized winding for a period of-approximately one-million cycles .within a time-duration of less than 10 seconds,

and immediately withdrawing said ferrous rod from said winding and subjecting the thus-treated portion thereof to the action of forging dies beforerappreciable scale formation can occur.A

HAROLD F. HovvARD.l WILLIAM RICHARDS. 

